A family of molecular nickel hydrogen evolution catalysts providing tunable overpotentials using ligand-centered proton-coupled electron transfer paths

Abstract

The overpotential for H2 evolution from water can be rationally controlled by tuning the ligand-centered proton-coupled electron transfer (PCET) processes.

Ligand‐Based PCET Reduction in a Heteroleptic Ni(bpy)(dithiolene) Electrocatalyst Giving Rise to Higher Metal Basicity Required for Hydrogen Evolution

“…), choice of other more stable sulfur‐donating ligands may help researchers to advance the studies on the metal‐sulfur systems. In this context, researchers attempting to explore artificial hydrogenase mimics have paid great attention to dithiolene ligands (L; examples are shown in Scheme a) in order to examine the catalytic activity of various homoleptic ML 2 ‐type complexes with M=Fe, Co, Ni, Mo, Rh, and W ,. We also reported on the electrocatalytic activity of several NiL 2 ‐type complexes, showing their unique reaction paths permitting the formation of hydride intermediates via two consecutive ligand‐based proton‐coupled electron transfer (PCET) processes (Scheme (3)) ,,…”

“…In this context, researchers attempting to explore artificial hydrogenase mimics have paid great attention to dithiolene ligands (L; examples are shown in Scheme 1a) in order to examine the catalytic activity of various homoleptic ML 2 -type complexes with M=Fe, [18][19][20] Co, [21][22][23][24] Ni, [25][26][27][28][29][30][31][32][33] Mo, [34] Rh, [35] and W. [36,37] We also reported on the electrocatalytic activity of several NiL 2 -type complexes, showing their unique reaction paths permitting the formation of hydride intermediates via two consecutive ligand-based proton-coupled electron transfer (PCET) processes (Scheme 2(3)). [30,32,33] On the other hand, our previous efforts involve mechanistic studies on the HER catalyzed by various artificial systems with different metal and ligand geometries. The platinum(II) catalysts, such as PtCl 2 (bpy) derivatives (bpy = 2,2'-bipyridine), are important examples shown to give a hydridoplatinum(III) intermediate via a metal-ligand-centered PCET pathway, [38] depicted in Scheme 2(2).…”

Recent advances in the mechanisms of the hydrogen evolution reaction by non-innocent sulfur-coordinating metal complexes

“…152 Complexes 25 and 26, where the π-system of the pyrazine ring is extended, were also synthesized and their catalytic performances in aqueous solutions were evaluated and compared. 153 Indeed, complexes 25 and 26 achieve overpotential values of 0.17 V and 0.23 V, respectively, at pH 9.0, which indicates a large stabilization of the PCET state when compared to complex 23. The stabilization can be attributed to the formation of thioamide resonance structures, where the electron density is delocalized among the metal, the ligating sulfur atoms and the protonated nitrogen atoms.…”

“…154 Notably, under higher overpotential conditions, the catalytic efficiencies of 25 and 26 increase considerably, possibly because different reac-tion pathways are thermodynamically favored under more negative potentials. 153…”

Cu[Ni(2,3-pyrazinedithiolate)2] Metal–Organic Framework for Electrocatalytic Hydrogen Evolution

“…Although Cu­[Ni­(pdt) 2 ] has been studied for applications in gas separation, , its electrocatalytic applications remain underdeveloped. In contrast, the electrocatalytic HER performance of the molecular analogues of this material has been extensively explored. − In one of the prior reports, a [Ni­(dcpdt) 2 ] 2– (dcpdt = 5,6-dicyanopyrazine-2,3-dithiolate) complex was shown to perform HER with low overpotentials (330–400 mV) and high faradic efficiencies (92–100%) in pH 4–6 aqueous solutions . The excellent HER activity of these molecular complexes prompted us to explore the competency of Cu­[Ni­(pdt) 2 ], where the Ni-dithiolene active units are incorporated into a 3D framework, allowing for the transitioning from homogeneous to heterogeneous catalysis.…”